The present invention addresses two problems associated with the operational voltage (i.e., the power supply voltage) of today's microprocessors and other integrated circuit devices (ICs). First, the operational voltages of today's microprocessors are progressively being decreased in order to optimize performance and reduce power consumption. Reducing the operational voltage permits down-scaling of a microprocessor's transistors which helps to provide higher frequency operation. This "decreasing operational voltages" problem mainly affects board designers and computer manufacturers because each decrease requires costly changes to existing computer system designs in order to provide the new operational voltages. Second, having to guarantee microprocessor operation over a full range of voltage and temperature specifications limits the upper frequency specification of IC devices. This "full voltage range specification" problem mainly affects microprocessor manufacturers by limiting the high-end speed performance of their microprocessors. These problems, however, are not unique to microprocessors but are associated to some degree with all integrated circuit devices. Each problem will now be discussed in more detail.
Decreasing Operational Voltages Problem. Computers and other digital devices include a variety of individual ICs. For example, a personal computer, such as an IBM PC.TM. computer, or compatible type computer, typically includes a microprocessor, memory chips, various peripheral controller chips, video display chips, etc. Each IC requires electrical power. A PC also includes a power supply for supplying various supply voltages to the ICs. A typical PC power supply provides voltages of .+-.5.0 and .+-.12.0 volts. Traditionally, a PC's microprocessor has operated at the .+-.5.0 volt supply voltage.
Today the operational voltage of microprocessors are progressively being reduced in order to help increase microprocessor performance and reduce power consumption to increase battery life of laptop and notebook computers. Reducing the operational voltage helps to provide increased performance because at the reduced voltage the microprocessor's transistors can be scaled to smaller sizes which are capable of operating at higher frequencies. For example, a 3.3 volt version of the i486.TM. microprocessor available from Intel Corporation of Santa Clara, California is currently available and future versions operating at 2.5 volts and 1.8 volts are already planned. Previously, Intel architecture microprocessors were only available in 5.0 volt versions.
But along with the benefits of reduced power consumption, decreasing the operational voltage of today's microprocessors poses problems for both computer system manufacturers and microprocessor manufacturers. For computer manufacturers, one problem is having to redesign their computer systems with a new power supply to provide the new supply voltage. For microprocessor manufacturers, one problem is having to provide multiple versions of their microprocessors, one that operates at the reduced voltage and another that operates at the old voltage, because not all computer manufacturers are able to change to the reduced voltage microprocessors.
Full Voltage Range Specification Problem. The highest frequency, or highest speed, of reliable operation speed of an integrated circuit device changes with the supply voltage and the temperature of the device. For example, at a constant temperature a microprocessor's maximum frequency typically increases with increasing supply voltage (within the operational range). At a constant supply voltage a microprocessor's maximum frequency typically decreases with increasing temperature. Therefore, a typical microprocessor is slowest when operating at low voltage and high temperature and fastest when operating at high voltage and low temperature.
Today, microprocessor manufacturers specify a guaranteed range of supply voltages and temperatures over which their microprocessors are guaranteed to operate at a specified upper frequency. For example, one version of Intel's i486.TM. microprocessor is specified to operate at 66 MHz over a temperature range of 0.degree.-85.degree. C. and a power supply voltage range of 5.0.+-.0.25 volts. Another version of Intel's i486.TM. microprocessor is specified to operate at 66 MHz over a temperature range of 0.degree.-85.degree. C. and a power supply voltage range of 3.3.+-.0.3 volts.
Having to guarantee microprocessor operation over a full range of supply voltages and temperatures unduly limits the upper frequency specification because only certain supply voltage and temperature combinations exhibit slower performance. If the frequency-limiting supply voltage and temperature combinations (such as low voltage and high temperature) could be avoided, the upper frequency specification of the microprocessor could be increased, thereby providing higher performance microprocessors.
Considering the foregoing problems, an integrated circuit device that selects its own supply voltage by controlling a power supply is needed.